A handful of people have been killed in Sudan during protests over living costs that have been spreading through the country on Thursday.

Authorities declared a state of emergency and curfew in al-Qatarif, according to a local official cited by Reuters.

The move followed another state of emergency imposed by the Nile River state on the northeastern state of Atbara, which has been the focal point of the protests since demonstrators torched the ruling National Congress Party's local offices on Wednesday.

The number of people killed in these protests vary slightly, with AFP alleging that six people have died whereas Reuters, citing a local TV broadcast, have said that eight people have been killed.

Six people died in demonstrations in al-Qadarif, Reuters said, citing the city's commissioner comments to private channel Sudania 24 private TV channel. Two people died in Nile River state, a spokesman for the state told the same channel.

Tear gas has been used to disperse protesters on Thursday, including a crowd of 500 people who were gathered a kilometre from the presidential palace in the capital Khartoum.

Anger at many of the protests has been directed against President Omar al-Bashir, calling for the fall of his government.

Despite the state of emergency thousands came out on the streets of Atbara again on Thursday and the Sudania 24 channel showed images of the National Congress Party offices in the city of Dongola engulfed in flames.

"The situation in Al-Qatarif is out of control and the student Moayed Ahmad Mahmoud was killed," said Mubarak al-Nur, a lawmaker who called for security forces not to use force on protesters, who should "peacefully exercise their right".

Sadiq al-Mahdi, a leading opposition figure, returned to Sudan on Wednesday after nearly a year in self-imposed exile.

"I went out to protest because life has stopped in Atbara," a 36-year-old man, who participated in Wednesday's demonstration and asked not to be named, told Reuters on Thursday.

He said he had not been able to buy bread for four days because it was no longer available in the shops.

"Prices have increased and I have still not been able to withdraw my November salary... because of the liquidity crisis. These are difficult conditions that we can't live with, and the government doesn't care about us."

Small protests led by students have sporadically started in different parts of Sudan throughout December, with Radio Dabanga reporting that callers from across the country had said additional police officers had been deployed in anticipation of larger protests.

"The protests began peacefully and then turned to violence and vandalism," Hatem al-Wassilah, governor of the Nile River state, said of Wednesday's demonstrations on Sudania 24.

Sudan's economy was hit hard when the south of the country seceded in 2011. With the secession, Sudan lost three-quarters of its oil output, a crucial source of foreign currency.

In October, Sudan sharply devalued its currency after the government asked a body of banks and money changers to set the exchange rate on a daily basis.

The move led to further price increases and a liquidity crunch, while the gap between the official and black market rates has continued to widen.

At least three people were killed during similar protests against rising bread prices in January.

Sudanese Prime Minister Motazz Moussa tried to reassure citizens on Wednesday, denying bread subsidies would be lifted as part of the austerity measures.

"There will be no lifting of subsidies," Moussa said. "But there will be new policies to direct subsidies to the deserving, as we cannot subsidise the financially able."

He said Sudan's budget for 2019 includes 66bn Sudanese pounds ($1.4bn) in subsidies, with a vast majority of that sum - $1.1bn - allocated to fuel and bread.

Nicknamed the "City of Steel and Fire," the town of Atbara is historically significant for Sudanese workers because it was at the centre of the country's railway system.

The town was home to an active railway workers' union until it was dismantled in the 1980s under the rule of President Gaafar Nimeiry, who came to power in the 1969 military coup.